As is disclosed in Japanese Patent No. 3331987 (U.S. Pat. No. 6,209,515B1), there has been well known a control apparatus that has a cylinder pressure sensor for detecting pressure in a combustion chamber mounted on only a cylinder, in which the quantity of exhaust gas recirculated (EGR) into an intake passage from an exhaust passage is the largest, and controls injection start timings of all cylinders on the basis of the pressure detected by the cylinder pressure sensor. Here, in view of the fact that combustion tends to easily become unstable in a cylinder having the largest quantity of EGR, the cylinder pressure sensor is mounted only on the cylinder having the largest quantity of EGR. With this, an ignition timing of a cylinder in which combustion tends to become most unstable can be directly found on the basis of the detection result of the cylinder pressure sensor, which in turn makes it possible to avoid mounting all cylinders with cylinder pressure sensors and to control the injection timings of all cylinders so as not to cause a misfire.
However, in the foregoing control apparatus, when the state of inflow of the quantity of EGR of each cylinder is changed by the secular change or the like of the internal combustion engine, if the ignition timings of all cylinders are controlled in the manner described above, depending on a cylinder, there can be developed an event in which the ignition timing of the cylinder is not suitable. When an internal combustion engine has a cylinder of which ignition timing is not suitable, the exhaust characteristics of the internal combustion engine is impaired or the drivability of a vehicle mounted with the internal combustion engine is reduced.